Bug#1096138: libsdl2-dev: audio capture with pulseaudio do not work

[Petter Reinholdtsen]

[Simon McVittie]
> It would probably be useful to let upstream know that this regressed
> somewhere between 2.28.0 and commit 38d11e5c: that might be helpful when
> narrowing down what change caused this.

It is already reported in the forwarded issue.

I investigated further, and now believe the problem is in the
PULSEAUDIO_FlushCapture(), which seem to be unable to flush the data
faster than pulseaudio is producing data, causing it to keep flushing
while the client is waiting for audio.  The following patch solved the
problem for the test program, by recording up front how much data to
flush, and then stop flushing once at least that amount has been
dropped.

diff --git a/src/audio/pulseaudio/SDL_pulseaudio.c b/src/audio/pulseaudio/SDL_pulseaudio.c
index 2fb2f31c6..d434a35e2 100644
--- a/src/audio/pulseaudio/SDL_pulseaudio.c
+++ b/src/audio/pulseaudio/SDL_pulseaudio.c
@@ -497,7 +497,7 @@ static void PULSEAUDIO_FlushCapture(_THIS)
 {
     struct SDL_PrivateAudioData *h = this->hidden;
     const void *data = NULL;
-    size_t nbytes = 0;
+    size_t nbytes = 0, buflen = 0;
 
     PULSEAUDIO_pa_threaded_mainloop_lock(pulseaudio_threaded_mainloop);
 
@@ -507,18 +507,20 @@ static void PULSEAUDIO_FlushCapture(_THIS)
         h->capturelen = 0;
     }
 
-    while (SDL_AtomicGet(&this->enabled) && (PULSEAUDIO_pa_stream_readable_size(h->stream) > 0)) {
+    buflen = PULSEAUDIO_pa_stream_readable_size(h->stream);
+    while (SDL_AtomicGet(&this->enabled) && (buflen > 0)) {
         PULSEAUDIO_pa_threaded_mainloop_wait(pulseaudio_threaded_mainloop);
         if ((PULSEAUDIO_pa_context_get_state(pulseaudio_context) != PA_CONTEXT_READY) || (PULSEAUDIO_pa_stream_get_state(h->stream) != PA_STREAM_READY)) {
             /*printf("PULSEAUDIO DEVICE FAILURE IN FLUSHCAPTURE!\n");*/
             SDL_OpenedAudioDeviceDisconnected(this);
             break;
         }
-
-        if (PULSEAUDIO_pa_stream_readable_size(h->stream) > 0) {
+        if (buflen > 0) {
+            /*printf("pulseaudio device flushcapture loop dump frament size=%ld\n", buflen);*/
             /* a new fragment is available! Just dump it. */
             PULSEAUDIO_pa_stream_peek(h->stream, &data, &nbytes);
             PULSEAUDIO_pa_stream_drop(h->stream); /* drop this fragment. */
+            buflen -= nbytes;
         }
     }
 


I will pass it upstream too.
-- 
Happy hacking
Petter Reinholdtsen